1. Field of the Invention
The present invention relates to a level switch, and more particularly to a rotary paddle level switch applied to detect material level of warehouse.
2. Description of the Related Art
Level switches are applicable to material management of warehouse, and serve to monitor the availability of material in warehouse or to detect the level of material stored in warehouse. The material in a warehouse may be any kind of material with a constant specific weight, such as, animal feed, grain, peanut, malt, clay, sand, limestone, rock, sawdust, lumber, metal, rubber, resin, plastic pellet, regrinding plastic, coal, cast material, and the like. Level switches can be classified as rotary paddle level switches, vibrating fork level switches, and capacitive level switches according to design concepts of the level switches.
A conventional rotary paddle level switch has a housing, a driving unit, a first switch, a second switch, a torque spring, a transmission shaft, and a propeller. The driving unit is pivotally mounted inside the housing, and has a pressing rod mounted away an axial direction and extending in an eccentric direction. The two switches are mounted inside the housing. One end of the torque spring abuts against an inner wall of the housing, and the other end of the torque spring pushes against the pressing rod such that the pressing rod abuts against the first switch. The transmission shaft is driven by the driving unit, and protrudes beyond the housing. The propeller is mounted on an external end of the transmission shaft.
When the conventional rotary paddle level switch is mounted in a warehouse and is operated, the driving unit drives the transmission shaft to rotate the propeller. When the level of a stored material rises up to reach the propeller, the propeller and the transmission shaft stop rotating because of the resistance caused by the material, and the driving unit compresses the torque spring to reversely rotate the transmission shaft. The pressing rod of the driving unit then departs from the first switch and abuts against the second switch instead. The driving unit stops rotating the transmission shaft after the pressing rod no longer abuts against the first switch. The second switch signals that the material has been accumulated to a designated level after being abutted, so as to achieve the objective of monitoring the level of a material stored in a warehouse.
However, the conventional rotary paddle level switch has the following shortcomings.
Firstly, during the course of dropping a material in a warehouse, the material may hit the propeller from a specific angle to abruptly rotate the propeller at a high speed. Rotating at a high speed, the parts of the driving unit, such as transmission gears, are prone to damage. A clutch is therefore mounted between the transmission shaft and the driving unit. When the propeller and the transmission shaft are subject to an excessively large external force, the clutch disconnects the transmission shaft from the driving unit to prevent the driving unit from being damaged. However, the conventional clutch is structurally complicated, and the production cost of the clutch is relatively high.
Secondly, when the propeller hits the accumulated material and generates a resistance force, the resistance force generates a torque that is indirectly exerted on the torque spring. However, the sensitivity and accuracy of the torque spring are not as satisfactory as expected, early or late deactivation of the driving unit.